System and method for locating wimax or lte subscriber stations

ABSTRACT

A system and method for estimating a location of a subscriber station receiving a first signal from a first base station and receiving a second signal from a second base station where the first and second base stations are nodes in a WiMAX or LTE network. A message may be received from the subscriber station containing first and second information, and a range ring determined from the first base station using the first information. A location hyperbola may be determined using the second information wherein the location hyperbola has the first and second base stations as foci. A location of the subscriber station may be estimated using the range ring and the location hyperbola.

RELATED APPLICATIONS

The instant application is a PCT national phase application of andclaims priority benefit of PCT International Application NumberPCT/US2009/043648 having an international filing date of 12 May 2009 andentitled “System and Method for Locating WiMAX or LTE SubscriberStations”, which claims priority benefit of U.S. Provisional ApplicationNo. 61/055,658, entitled, “WiMAX Mobile Location Method,” filed 23 May2008, the entirety of each is hereby incorporated herein by reference.Additionally, the instant application is related to and concurrentlyfiled with U.S. application Ser. No. ______ (AND01 100 US1) and U.S.application Ser. No. ______ (AND01 100 US2) each of which claim prioritybenefit of PCT International Application Number PCT/US2009/043648 andU.S. Provisional Application No. 61/055,658, the entirety of each of theabove-mentioned applications is hereby incorporated herein by reference.

BACKGROUND

The location of a mobile, wireless or wired device is a useful andsometimes necessary part of many services. A Location Information Server(“LIS”) may be responsible for providing location information to suchdevices with an access network. The LIS may utilize knowledge of theaccess network and its physical topology to generate and serve locationinformation to devices.

The LIS, in general terms, is a network node originally defined in theNational Emergency Number Association (“NENA”) 12 network architectureaddressing a solution for providing E-911 service for users of Voiceover Internet Protocol (“VoIP”) telephony. In VoIP networks, the LIS isthe node that determines the location of the VoIP terminal. Beyond theNENA architecture and VoIP, the LIS is a service provided by an accessnetwork provider to supply location information to users of the networkby utilizing knowledge of network topology and employing a range oflocation determination techniques to locate devices attached to thenetwork. The precise methods used to determine location are generallydependent on the type of access network and the information that can beobtained from the device. For example, in a wired network, such asEthernet or DSL, a wiremap method is commonplace. In wiremap locationdetermination, the location of a device may be determined by findingwhich cables are used to send packets to the device. This involvestracing data through aggregation points in the network (e.g., Ethernetswitches, DSL access nodes) and finding the port for which packets aresent to the device. This information is combined with data available tothe LIS (generally extracted from a database) to determine a finallocation of the device.

In wireless networks, a range of technologies may be applied forlocation determination, the most basic of which uses the location of theradio transmitter as an approximation. The Internet Engineering TaskForce (“IETF”) and other standards forums have defined variousarchitectures and protocols for acquiring location information from anLIS. In such networks, an LIS may be automatically discovered andlocation information retrieved using network specific protocols.Location information may be retrieved directly or the LIS may generatetemporary uniform resource identifiers (“URI”) utilized to providelocation indirectly (i.e., location URI). Geodetic, civic positions andlocation URIs for a mobile device may be determined as a function oflocation information from the LIS. A request for geodetic and/or civiclocations may provide location information at the time the locationrequest is made. A location URI may generally be passed to another partywhich can utilize it to retrieve the target device's location at a latertime, typically from the same location server that provided the locationURI.

A few exemplary wireless networks are a World Interoperability forMicrowave Access (“WiMAX”) network and a Long Term Evolution (“LTE”)network. Generally, WiMAX is intended to reduce the barriers towidespread broadband access deployment with standards-compliant wirelesssolutions engineered to deliver ubiquitous fixed and mobile servicessuch as Voice over IP (“VoIP”), messaging, video, streaming media, andother IP traffic. WiMAX enables delivery of last-mile broadband accesswithout the need for direct line of sight. Ease of installation, widecoverage, and flexibility makes WiMAX suitable for a range ofdeployments over long-distance and regional networks, in addition torural or underdeveloped areas where wired and other wireless solutionsare not easily deployed and line of sight coverage is not possible.

LTE is generally a 4G wireless technology and is considered the next inline in the GSM evolution path after UMTS/HSPDA 3G technologies. LTEbuilds on the 3GPP family including GSM, GPRS, EDGE, WCDMA, HSPA, etc.,and is an all-IP standard like WiMAX. LTE is based on orthogonalfrequency division multiplexing (“OFDM”) Radio Access technology andmultiple input multiple output (“MIMO”) antenna technology. LTE provideshigher data transmission rates while efficiently utilizing the spectrumthereby supporting a multitude of subscribers than is possible withpre-4G spectral frequencies. LTE is all-IP permitting applications suchas real time voice, video, gaming, social networking and location-basedservices. LTE networks may also co-operate with circuit-switched legacynetworks and result in a seamless network environment and signals may beexchanged between traditional networks, the new 4G network and theInternet seamlessly.

The original version of the standard on which WiMAX is based (IEEE802.16) specified a physical layer operating in the 10 to 66 GHz range.802.16a, updated in 2004 to 802.16-2004, added specifications for the 2to 11 GHz range. 802.16-2004 was updated by 802.16e-2005 in 2005 anduses scalable orthogonal frequency division multiple access (“SOFDMA”)as opposed to the OFDM version with 256 sub-carriers (of which 200 areused) in 802.16d. More advanced versions, including 802.16e, also bringMultiple Antenna Support through MIMO functionality. This bringspotential benefits in terms of coverage, self installation, powerconsumption, frequency re-use and bandwidth efficiency. Furthermore,802.16e also adds a capability for full mobility support. Mostcommercial interest is in the 802.16d and 802.16e standards, since thelower frequencies used in these variants suffer less from inherentsignal attenuation and therefore gives improved range and in-buildingpenetration. Already today, a number of networks throughout the worldare in commercial operation using WiMAX equipment compliant with the802.16d standard.

The WiMAX Forum has provided an architecture defining how a WiMAXnetwork connects with other networks, and a variety of other aspects ofoperating such a network, including address allocation, authentication,etc. It is important to note that a functional architecture may bedesigned into various hardware configurations rather than fixedconfigurations. For example, WiMAX architectures according toembodiments of the present subject matter are flexible enough to allowremote/mobile stations of varying scale and functionality and basestations of varying size. The art of WiMAX and LTE subscriber station(SS) location, however, is still in its infancy, and the currentstandards do not define how to solve the WiMAX and LTE location problemsusing network measurement messages utilized by the respective networksfor normal operation. Thus, there is a need in the art to overcome thelimitations of the prior art and provide a novel system and method forlocating WiMAX and LTE subscriber stations.

One embodiment of the present subject matter provides a method forestimating a location of a subscriber station receiving a first signalfrom a first base station and receiving a second signal from a secondbase station where the first and second base stations are nodes in aWiMAX or LTE network. The method may comprise receiving from thesubscriber station a message containing a first information and a secondinformation, and determining a range ring from the first base stationusing the first information. A location hyperbola may be determinedusing the second information wherein the location hyperbola has thefirst and the second base stations as foci. A location of the subscriberstation may then be estimated using the range ring and locationhyperbola.

Another embodiment of the present subject matter may provide a methodfor estimating a location of a subscriber station receiving a firstsignal from a first base station, receiving a second signal from asecond base station, and receiving a third signal from a third basestation where the first, second, and third base stations are nodes in aWiMAX or LTE network. The method may comprise receiving from thesubscriber station a message containing a first information and a secondinformation, and determining a range ring from the first base stationusing the first information. A location hyperbola may be determinedusing the second information wherein the location hyperbola has thesecond and the third base stations as foci. A location of the subscriberstation may then be estimated using the range ring and the locationhyperbola.

A further embodiment of the present subject matter provides a method forestimating a location of a subscriber station receiving a signal from abase station where the base station is a node in a WiMAX or LTE network.The method may comprise receiving from said subscriber station a messagecontaining a first information and a second information, and determininga range ring from the base station using the first information. Aserving sector of the base station may be determined for the subscriberstation, and plural sub-sectors determined for the serving sector. Fromthe second information a carrier-to-interference noise ratio (“CINR”)may be determined for each of a first and a second neighboring sector tothe serving sector. A most likely sub-sector may also be determined fromthe plural sub-sectors based on a comparison of the CINR for the firstand second neighboring sectors. A location of the subscriber station maythen be estimated as a point of intersection of the range ring and abisector of the most likely sub-sector.

One embodiment of the present subject matter provides a method forestimating a location of a subscriber station operating in a wirelessnetwork. The method may comprise the steps of transmitting from anetwork location device to a first base station a request for networkmeasurement data, and transmitting from the first base station to thesubscriber station a message to trigger the subscriber station to scanthe wireless network. A scanning result message containing informationcharacterizing the first base station and a second base station may betransmitted from the subscriber station to the first base station, andinformation from the scanning result message transmitted from the firstbase station to the network location device. A location for thesubscriber station may then be estimated at the network location devicebased at least on the information from the scanning result message.

A further embodiment of the present subject matter provides a system forestimating a location of a subscriber station receiving a first signalfrom a first base station and receiving a second signal from a secondbase station where the first and second base stations are nodes in aWiMAX or LTE network. The system may include a receiver for receivingfrom the subscriber station a message containing a first information anda second information, and circuitry for determining a range ring fromthe first base station using the first information. The system may alsoinclude circuitry for determining a location hyperbola using the secondinformation wherein the location hyperbola has the first and second basestations as foci. The system may include circuitry for estimating alocation of the subscriber station using the range ring and the locationhyperbola.

Another embodiment of the present subject matter provides a system forestimating a location of a subscriber station receiving a first signalfrom a first base station, receiving a second signal from a second basestation, and receiving a third signal from a third base station wherethe first, second, and third base stations are nodes in a WiMAX or LTEnetwork. The system may comprise a receiver for receiving from thesubscriber station a message containing a first information and a secondinformation, and circuitry for determining a range ring from the firstbase station using the first information. The system may also comprisecircuitry for determining a location hyperbola using the secondinformation wherein the location hyperbola has the second and third basestations as foci. The system may comprise circuitry for estimating alocation of the subscriber station using the range ring and locationhyperbola.

Yet another embodiment of the present subject matter provides a systemfor estimating a location of a subscriber station receiving a signalfrom a base station where the base station is a node in a WiMAX or LTEnetwork. The system may comprise a receiver for receiving from thesubscriber station a message containing a first information and a secondinformation, and circuitry for determining a range ring from the basestation using the first information. The system may also includecircuitry for determining a serving sector of the base station for thesubscriber station, and circuitry for determining plural sub-sectors forthe serving sector. The system may include circuitry for determiningfrom the second information a CINR for each of a first and a secondneighboring sector to the serving sector, and circuitry for determininga most likely sub-sector from the plural sub-sectors based on acomparison of the CINR for the first and second neighboring sectors. Thesystem may further include circuitry for estimating a location of thesubscriber station as a point of intersection of the range ring and abisector of the most likely sub-sector.

One embodiment of the present subject matter provides a system forestimating a location of a subscriber station operating in a wirelessnetwork. The system may include a network location device including afirst transmitter for transmitting to a first base station a request fornetwork measurement data where the first base station includes a secondtransmitter to transmit to the subscriber station a message to triggerthe subscriber station to scan the wireless network. The subscriberstation may include a third transmitter to transmit to the first basestation a scanning result message containing information characterizingthe first base station and a second base station. The first base stationmay include a fourth transmitter to transmit to the network locationdevice information from the scanning result message. The system may alsoinclude circuitry for estimating at the network location device alocation for the subscriber station based at least on the informationfrom the scanning result message.

These embodiments and many other objects and advantages thereof will bereadily apparent to one skilled in the art to which the inventionpertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present disclosure will be or become apparent toone with skill in the art by reference to the following detaileddescription when considered in connection with the accompanyingexemplary non-limiting embodiments.

FIGS. 1A-1C are diagrams of Internet location services models.

FIG. 2 is a diagram of an exemplary access network model.

FIG. 3 is a high level diagram of one embodiment of the present subjectmatter.

FIG. 4 is a more detailed diagram of an exemplary WiMAX Location BasedService network architecture.

FIG. 5 is a diagram of a call flow according to one embodiment of thepresent subject matter.

FIG. 6 is a diagram of one embodiment of the present subject matter.

FIG. 7 is a diagram of another embodiment of the present subjectillustrating location estimation with two site hearability and sectorinformation.

FIG. 8 is a diagram of a further embodiment of the present subjectmatter illustrating location estimation with two site hearability andsub-sector information.

FIG. 9 is diagram of timing relationships in an embodiment of thepresent subject matter.

FIG. 10 is a schematic representation of an algorithm according to oneembodiment of the present subject matter.

FIG. 11 is a schematic representation of an algorithm according toanother embodiment of the present subject matter.

FIG. 12 is a schematic representation of an algorithm according to afurther embodiment of the present subject matter.

FIG. 13 is a schematic representation of an algorithm according to anadditional embodiment of the present subject matter.

DETAILED DESCRIPTION

With reference to the figures where like elements have been given likenumerical designations to facilitate an understanding of the presentsubject matter, the various embodiments of a system and method forlocating a WiMAX or LTE subscriber station are herein described.

Generally, a WiMAX or LTE subscriber station may provide to acommunications network round trip delay (“RTD”) information of an anchorbase station's downlink and uplink signals and the observed relativedelays of the neighboring base stations' downlink and uplink signals.The phrases subscriber station and mobile station are usedinterchangeably throughout this document and such should not limit thescope of the claims appended herewith. Further, the terms station anddevice are used interchangeably throughout this document and such shouldnot limit the scope of the claims appended herewith. The respectiveWiMAX or LTE network may utilize this data for hand-off operations;however, embodiments of present subject matter may determine from thisdata a range ring from the anchor or serving base station (“BS”) andlocation hyperbolas between the reported BSs, if the BS timings areknown.

As generally discussed above, the Location Information Server (“LIS”) isa network server that provides devices with information about theirlocation. The phrases and respective acronyms of Location InformationServer (“LIS”) and Location Server (“LS”) are used interchangeablythroughout this document and such should not limit the scope of theclaims appended herewith. Devices that require location information areable to request their location from the LIS. In the architecturesdeveloped by the IETF, NENA and other standards forums, the LIS may bemade available in an IP access network connecting one or more targetdevices to the Internet. In other modes of operation, the LIS may alsoprovide location information to other requesters relating to a targetdevice. To determine location information for a target device, anexemplary LIS may utilize a range of methods. The LIS may use knowledgeof network topology, private interfaces to networking devices likerouters, switches and base stations, and location determinationalgorithms. Exemplary algorithms may include known algorithms todetermine the location of a mobile device as a function of satelliteinformation, satellite assistance data, various downlink or uplinkalgorithms such as, but not limited to, time difference of arrival(“TDOA”), time of arrival (“TOA”), angle of arrival (“AOA”), round tripdelay (“RTD”), signal strength, advanced forward link trilateration(“AFLT”), enhanced observed time difference (“EOTD”), observed timedifference of arrival (“OTDOA”), uplink-TOA and uplink-TDOA, enhancedcell/sector and cell-ID, etc., and hybrid combinations thereof.

A location server according to an embodiment of the present subjectmatter may utilize a range of inputs to determine location informationfor the target device. For example, from a request made of the locationserver, the location server may determine one or more parameters, e.g.,Internet Protocol (“IP”) and Media Access Control (“MAC”) addresses,that uniquely identify the target mobile device. This identificationinformation may be used as an input to an exemplary measurementcollection process that produces further information in the form ofmeasurements or measurement results. Measurement information may also bedata already known to the location server, additional parameters thatidentify the target mobile device in other ways, and/or parametersrelating to the network attachment of the target mobile device.Non-limiting examples include the MAC address of the device, theidentity of network nodes from which network traffic to and from thedevice transits (including any physical connections involved), thelocation of network intermediaries (e.g., wiring maps), radio timing,signal strength measurements and other terrestrial radio frequencyinformation, and network configuration parameters, to name a few.

Protocols such as Flexible LIS-ALE Protocol (“FLAP”) are being developedin the Alliance for Telecommunications Industry Solutions (“ATIS”) forumto provide a formal definition of location-related measurements fordifferent types of access networks. FLAP generally facilitates transferof values of location measurement parameters from a network to the LISto enable the latter to compute the location of an IP end-device. TheLIS may interact with an Access Location Entity (“ALE”) residing in anaccess network to retrieve location measurements. Location informationmay be retrieved directly or the LIS may generate temporary uniformresource identifiers (“URI”) utilized to provide location indirectly(i.e., location URI). Geodetic, civic positions and location URIs for amobile device may be determined as a function of location informationfrom the US.

There are many models in which an LIS may be utilized. For example,FIGS. 1A-1C provide three examples of an Internet location servicesmodel for an LIS. With reference to FIG. 1A, a location by value modelis provided in which a target or mobile device 110 may obtain a locationfrom a location server 120 in a respective access network or domain 112.The device 110 may then convey its location to a location based service130 in the service domain 132 using an appropriate application protocol.With reference to FIG. 1B, a location by reference model is provided inwhich a mobile device 110 may obtain a reference from the locationserver 120 in the respective access network or domain 112. The device110 may convey the reference to the location based service 130 in theservice domain using an appropriate application protocol. The service130 may then query the location server 120 direct for location valuesfor the device 110. Generally the protocol utilized for communicationbetween the device 110 and location server 120 is HTTP Enabled LocationDelivery (“HELD”) and the protocol utilized for communication betweenthe location server 120 and the service 130 is HELD. The protocolutilized for communication between the device 110 and the service 130 isapplication protocol dependent.

With reference to FIG. 1C, an on-behalf-of (“OBO”) location model isprovided in which a trusted third party application or service 140queries for the location of a device 110. A client identity, which isunderstood by the location server 120, may be used as a query parameter(e.g., IP or MAC address). If applicable, the third party 140 mayprovide location information to external service entities 130. If thelocation was requested and provided by reference, the external entity130 may query back to the location server 120 for location value updatesusing the HELD protocol. The above described Internet location servicesmodels illustrate how LIS clients may request and receive locationinformation from the LIS. The value of parameters derived from such acommunications network may be used by the device and may be used by theLIS to determine location. In order to make use of these parameters, itis necessary for their values to be transferred form the communicationnetwork elements to the LIS, which is one purpose of FLAP.

FIG. 2 is a diagram of an exemplary access network model. With referenceto FIG. 2, an exemplary access network model 200 may include one or moreLISs 202 connected to one or more access networks, 210-260. An accessnetwork refers to a network that provides a connection between a deviceand the Internet. This may include the physical infrastructure, cabling,radio transmitters, switching and routing nodes and servers. The accessnetwork may also cover services required to enable IP communicationincluding servers that provide addressing and configuration informationsuch as DHCP and DNS servers. Examples of different types of accessnetworks include, but are not limited to, DSL 210, cable 220, WiFi,wired Ethernet 230, WiMAX 240, cellular packet services 250, and 802.11wireless 260, LTE, among others. An exemplary LIS 202 may be implementedon multiple processing units, any one of which may provide locationinformation for a target device from a first site, a second site and/oradditional sites. Therefore, an exemplary LIS 202 may provide highavailability by having more than one processing unit at a first site andby having multiple processing units at a second site for copying orbackup purposes in the event a site or a processing unit fails.

FIG. 3 is a high level diagram of one embodiment of the present subjectmatter. With reference to FIG. 3, an exemplary wireless network orsystem 300 may include an LIS 302 in communication with one or more basestations (“BS”) 322, a positioning determining entity (“PDE”) 332, andone or more network synchronization units (“NSU”) 342. One or moremobile or subscriber stations or devices 310 may be in communicationwith the LIS 302 via the one or more BSs 322. A recipient or user 312 oflocation information may request the LIS 302 to locate a subscriberstation 310. The LIS 302 may then request the serving BS 322 to providenetwork measurement information. The BS 322 receives the data from thetarget subscriber station 310 and provides the data to the LIS 302. TheLIS 302 may, in one embodiment, send the data to the PDE 332 to computethe location of the target station or device 310. Once the location iscomputed, the LIS 302 may provide the location information to therequesting user 312.

FIG. 4 is a more detailed diagram of an exemplary WiMAX Location BasedService (“LBS”) network architecture 400. With reference to FIG. 4, theWiMAX forum defines a number of functional entities and interfacesbetween those entities. An exemplary network architecture 400 includesone or more access service networks (“ASN”) 420, each having one or morebase stations (“BS”) 422, 423 and one or more ASN gateways (“ASN-GW”)424 forming the radio access network at the edge thereof. One or moremobile stations or devices 410, such as a WiMAX device, having alocation requester 412 may be in communication with the ASN 420 via oneor more BSs 422, 423 over an R1 interface 401. BSs 422, 423 areresponsible for providing the air interface to the MS 410. Additionalfunctions may, of course, be part of BSs 422, 423, such as micromobilitymanagement functions, handoff triggering, tunnel establishment, radioresource management, QoS policy enforcement, traffic classification,Dynamic Host Control Protocol (“DHCP”) proxy, key management, sessionmanagement, and multicast group management, to name a few. BSs 422, 423communicate with one another via resident location agents (“LA”) 425over an R8 interface 408. LAs 425 are generally responsible formeasurements and reporting and may communicate with the device 410 tocollect measurements. BSs 422, 423 also communicate with the ASN-GWs 424via a location controller (“LC”) 426 in the ASN-GW 424 over an R6interface 406. LCs 426 generally trigger and collect locationmeasurements and forward these measurements to a location server (“LS”)in a selected connectivity service network (“CSN”) 430.

The ASN-GW 424 generally acts as a layer 2 traffic aggregation pointwithin an ASN 420. Additional functions that may be part of the ASN-GW424 include, but are not limited to, intra-ASN location management andpaging, radio resource management and admission control, caching ofsubscriber profiles and encryption keys, AAA client functionality,establishment and management of mobility tunnel with BSs, QoS and policyenforcement, foreign agent functionality for mobile IP and routing to aselected CSN. Communication between ASNs 420 occurs over an R4 interface404. It should also be noted that a Public Safety Answering Point(“PSAP”) or an Internet Application Service Provider (“iASP”) 440 mayalso include a location requester 442 and may be in communication with ahome CSN 434 over a U1 interface 444.

A third portion of the network includes the CSN 430. The CSN may be avisited network having a visited-CSN (“V-CSN”) 432 or a home networkhaving a home-CSN (“H-CSN”) 434, collectively CSNs 430. These CSNs 430provide IP connectivity and generally all the IP core network functionsin the network 400. For example, the CSN 430 provides connectivity tothe Internet, ASP, other public networks and corporate networks. The CSN430 is owned by a network service provider (“NSP”) and includesAuthentication Authorization Access (“AAA”) servers (home-AAA 438 andvisited-AAA 439 servers) that support authentication for the devices,users, and specific services. Similar to other networks, home andvisited AAA servers 438, 439 provide the following core functions in aWiMAX network: Authentication—Confirmation that a user requesting anetwork service is entitled to do so. This involves presentation of anidentity and credentials such as a user name, password, and/or digitalcertificate. This also requires support for device authentication;Authorization—The granting of specific types of service (or “noservice”) to a user based on his/her authentication, the servicesrequested, and the current system state; and Accounting—The tracking ofnetwork resource consumption by users. In the WiMAX Forum's NWG Stage 3Release 1.0.0 specification, AAA is specified as a basic building block.It also includes some functions that are not typically supported inother AAA deployments, such as Wi-Fi. This version of the standard isfocused on the use of AAA in Mobile WiMAX, including support for mobileIP. Fixed WiMAX, as well as Wi-Fi, conventionally utilizes RADIUS AAA,Extensible Authentication Protocol (“EAP”), or a custom authenticationmethod. Authorization attributes returned are similar to those returnedfor common Wi-Fi deployments.

The CSN 430 also provides per user policy management of QoS andsecurity. The CSN 430 is also responsible for IP address management,support for roaming between different NSPs, location management betweenASNs 420, and mobility and roaming between ASNs 420, to name a few.Communication between the ASN 420 and a CSN 430 occurs via therespective ASN-GW 424 over an R3 interface 403.

One entity within a CSN 430 is a LIS or location server (“LS”).Depending upon whether the device 410 is roaming and in directcommunication with a remote network or in direct communication with ahome network, the LS may be a visited-LS (“V-LS”) 436 or a home-LS(“H-LS”) 437. The role of the LS is to provide location informationabout a WiMAX device 410 in the network 400. Communication between theWiMAX device 410 and the LS 436, 437 is performed over an R2 interface402. The WiMAX forum explicitly allows the use of OMA SUPL 2.0 over theR2 interface 402. WiMAX provides a roaming architecture where a devicehas a home network but may connect to a network provided by a differentoperator, such as a visited network. In this mode of operation twolocation servers may exist, the H-LS 437 in the home network, and theV-LS 436 in the visited network. The WiMAX forum defines an interfacebetween the H-LS 437 and V-LS 436 called the R5 interface 405. The WiMAXforum, however, does not define how location requests are sent acrossthe R5 interface 405 other than they are RADIUS protocol messages orDIAMETER protocol messages.

It should be noted that there are several location determination methodssupported by the above-described network architecture 400. For example,a device 410, which is equipped with GPS capability may utilize 802.16mMAC and PHY features to estimate its location when GPS is not available,e.g., indoors, or be able to faster and more accurately acquire GPSsignals for location determination. The network 400 may make the GPSassistance data, including GPS Almanac data and Ephemeris data,available through broadcast and/or unicast air interface messages to thedevice 410. The delivery of GPS assistance data from the network 400 todevices 410 can be realized by enhanced GPS broadcast and/or unicastmessages and enhanced LBS management messages. Assisted GPS (“A-GPS”)may also be supported where an integrated GPS receiver and associatednetwork components assist a GPS device to speed up GPS receiver “coldstartup” procedure. For example, BSs 422, 423 may provide the device 410with the GPS Almanac and Ephemeris information downloaded from GPSsatellites. By having accurate, surveyed coordinates for the cell sitetowers, the BSs 422, 423 may also provide better knowledge ofionospheric conditions and other errors affecting the GPS signal thanthe device 410 alone, enabling more precise calculation of position.

Non-GPS-Based supported methods rely on the role of the serving andneighboring BSs or other components. For example, in a downlink (“DL”)scenario, a device 410 may receive existing signals (e.g., preamblesequence) or new signals designed specifically for the LBS measurements,if it is needed to meet the requirement from the serving/attached BS andmultiple neighboring BSs 422, 423. The BSs 422, 423 are able tocoordinate transmission of their sequences using different time slots ordifferent OFDM subcarriers. The device 410 accurately calculates therequired measurements, even in the presence of multipath channel andheavy interference environment, and then estimates its locationaccordingly. In an uplink (“UL”) scenario, various approaches may beutilized at the BSs 422, 423 to locate the device. Exemplarymeasurements are generally supported via existing UL transmissions(e.g., ranging sequence) or new signals designed specifically for theLBS measurements. Exemplary methods may include but are not limited to,TDOA, TOA, RTD, AOA, RSSI, Advanced forward link trilateration(“A-FLT”), Enhanced observed time difference (“EOTD”), Observed timedifference of arrival (“OTDOA”), time of arrival (“TOA”), uplink-TOA anduplink-TDOA, Enhanced cell/sector and cell-ID, etc., and hybridcombinations thereof.

FIG. 5 is a diagram of a call flow 500 according to one embodiment ofthe present subject matter. With reference to FIGS. 3-5, an LIS 302 mayreceive or supply a request for network measurement data to or from a BS322, 422 at step 510. The BS 322, 422 may periodically transmit aMOB_NBR-ADV management message to identify the network and define thecharacteristics of neighboring B Ss to a device or subscriber station310, 410 at step 520. At step 532, the BS 322, 422 transmits aMOB_SCN-RSP message to trigger mobile scan reporting. The subscriberstation 310, 410 may respond with a MOB_SCN-REP message including theRTD, relative delay, carrier to interference and noise ration (“CINR”),received signal strength indicator (“RSSI”) measurements, among others,and any GPS or A-GPS data, if available, on the downlink at steps 534and 540. At step 550, the BS 322, 422 may transmit the scanning resultand neighboring BS information along with a mapping table. In certainembodiments, the mapping table may be needed to convert some of the BSindices into 48-bit Base Station IDs (“BSID”). At step 560, the LIS 302may arrange the network measurement information for each 48-bit BSID,and at step 570 the LIS 302 may transmit the network measurementinformation to a PDE 332 to compute the location of the targetsubscriber station 310, 410. The PDE 332 may then respond with alocation estimate of the target subscriber station 310, 410 at step 580.

In certain embodiments of the present subject matter, both networkconfiguration parameters and dynamic measurement quantities may beneeded for location determination. For example, any one or combinationof the following BS related parameters may be utilized by an exemplaryPDE to estimate the location of a target subscriber station: BSID,azimuth information for each sector, and/or latitude/longitude of eachsector. Of course, these parameters are exemplary only and should not inany way limit the scope of the claims appended herewith. Theseparameters may be transmitted to the PDE periodically, by demand, and/orby event (e.g., when the network configuration changes). The subscriberstation may also provide the following information: subscriber ID, RTDcorresponding to the serving or anchor BS, OTDOA of detected downlinksignals, CINR that may be utilized as weights of the measurements in anexemplary location computation algorithm, and/or RSSI. Again, theseparameters are exemplary only and should not in any way limit the scopeof the claims appended herewith. Relevant information may also be foundin the Scanning Result Report (MOB_SCN-REP) message, e.g, BS CINR mean,BS RSSI mean, Relative Delay, BS RTD (for serving BS).

The exemplary information described above may be grouped into any numberof information sets. For example, in one embodiment the information maybe grouped into three sets such as N_current_BSs, N_Neighbor_BS_Index,and N_Neighbor_BS_Full. In this embodiment, a BS index to BSID mappingtable (available to the BS) and the MOB_NBR-ADV message may be utilizedto ascertain the full 48-bit BSID for the respective N_Neighbor_BS_Indexset. While it is unnecessary for the PDE to have knowledge of thesethree sets, the PDE may require knowledge of the BSIDs to determine towhich BS the set of measurements applies. For example, the data that theLIS may need to transmit to the PDE is shown below in Table 1.

TABLE 1 Syntax Notes Subscriber ID May be any type of identifier usedbetween the serving base station, LIS and PDE. numberOfDetectedBS Totalnumber of detected BS from the MOB_SCN-REP message for (j=0; j<numberOfDetectedBS; j++) BSID 48-bit BSID that uniquely identifies a BS;the following elements correspond to this BSID CINR BS CINR mean for thegiven BSID RSSI BS RSSI mean for the given BSID relativeDelay RelativeDelay for the given BSID RTD BS RTD, if applicable, for the BSID

Relative delays obtained from the mobile scanning report may bemeaningful if the downlink transmission time is known. One embodiment ofthe present subject matter may synchronize the downlink frame markers ofthe base stations with GPS. In this embodiment, the relative delays mayprovide TDOA location hyperbolas without any timing compensation. Inanother embodiment, free running downlink frame markers may be utilized,that is, no GPS synchronization is used. In this embodiment, thedownlink frame markers of the BSs may drift with time andsynchronization may be achieved by using a timing bank method or networksynchronization unit (“NSU”) method. In the timing bank method, forA-GPS enabled subscriber stations, an accurate subscriber stationlocation and subscriber station measurements may be obtainedsimultaneously. The timing offsets of the measured downlink signals atthe time of measurement may be estimated from this data. In the eventthere exist several A-GPS enabled subscriber stations in the network andif these subscriber stations frequently report both GPS locations andsubscriber station measurements, the timing drift may be tracked andsynchronization achieved. In the NSU method, one or more NSUs may bedeployed throughout the network at known locations to monitor thedownlink transmission time. These NSUs may or may not be co-located withBSs, and the NSUs may be sparsely deployed in the network.

In one embodiment, the NSUs may be GPS trained whereby the respectiveNSUs collect downlink signals, correlate against the known transmittedcodes in the signals, and determine the TOAs of the downlink framemarkers. The discrete Fourier transform (“DFT”) duality properties, timeand frequency shifts, and circular convolution and multiplication may beutilized for detecting the TOA. An exemplary detection algorithm isprovided below.

Y(k)=X(k)H(k)e ^((−j2πkΔn/N))  (1)

With reference to Equation (1), X(k), in the frequency domain,represents a known pattern transmitted on the k^(th) OFDMA downlinkchannel, H(k) represents a channel model for the k^(th) channel, Y(k)represents a received signal at the NSU, Δn represents timing shift insamples, and N represents the FFT size. Because of the propagation delayand different sampling instants of the signal, the received signal maybe a time shifted version of the transmitted signal. From thetime-frequency duality property of DFT, circular time shift may manifestas frequency shift in the received signal. Similarly, for the adjacentchannel k−1, the received signal may be represented below.

Y(k−1)=X(k−1)H(k−1)e ^((−j2π(k−1)Δn/N))  (2)

The detection metric, M(k), may thus be represented as:

$\begin{matrix}\begin{matrix}{{M(k)} = {{X(k)}{{Y^{\prime}(k)} \cdot \lbrack {{X( {k - 1} )}{Y^{\prime}( {k - 1} )}} \rbrack^{\prime}}}} \\{= {{\lbrack {{X(k)}{X^{\prime}(k)}} \rbrack \cdot \lbrack {{X( {k - 1} )}{X^{\prime}( {k - 1} )}} \rbrack \cdot \lbrack {{H^{\prime}(k)} \cdot {H( {k - 1} )}} \rbrack}^{({{- {j2\pi\Delta}}\; {n/N}})}}}\end{matrix} & (3)\end{matrix}$

Adjacent channel responses are expected to be similar, and, therefore itfollows that:

H(k)≈H(k−1)  (4)

With the assumption represented by Equation 4, Equation 3 may berewritten as:

M(k)≈|X(k)|² ·|X(k−1)|² |H(k)|² e ^((−j2πΔn/N))  (5)

With reference to Equation (5), the first two terms are generally knownconstants. The third term, H(k), may vary with channel condition and isrepresentative of channel fading. The exponential provides a timingoffset relative to an ideal sampling instant; therefore, the third andfourth terms together may provide detection quality and TOA of thedownlink signal.

In another embodiment of the present subject matter, synchronization maybe obtained as a function of GPS trained downlink signals havingconstant offsets between frame markers. For example, if BS clocks areGPS trained but the downlink frame markers are not aligned, a simplifiedtiming bank or sparsely deployed NSU(s) may be utilized to achievesynchronization.

Embodiments of the present subject matter may utilize any number oflocation computation algorithms or triangulation techniques dependingupon the number of cells reported in the scanning report, For example,in the event that a scanning report includes only the RTD value of theserving BS, the intersection of a sector axis azimuth and an estimatedrange ring may be utilized as the mobile or subscriber station location.In this embodiment, the accuracy of the location estimation may beenhanced as a function of the CINR and/or RSSI. FIG. 6 is a diagram ofone embodiment of the present subject matter. With reference to FIG. 6,the intersection of a range ring 610 and sub-sector axis 612 a-c may beidentified as the location(s) of the subscriber station 620 a-c. A cell600 of radius R may provide three sectors, α, β, and γ. The α sector mayfurther be divided into three sub-sectors, α1, α2, and α3, which may ormay not be equal. The estimated range of the mobile or subscriberstation may be represented as r. As exemplary algorithm may berepresented by the following pseudo-code:

-   -   If (CINR)_(γ) is in the scanning report, but (CINR)_(β) is not        or is very weak        -   Then choose the intersection of the range ring and the axis            of sub-sector α₁ as mobile's location    -   Else if (CINR)_(β) is in the scanning report, but (CINR)_(γ) is        not or is very weak        -   Then choose the intersection of the range ring and the axis            of sub-sector α₃ as mobile's location    -   Else choose the intersection of the range ring and the axis of        sub-sector α₂ as mobile's location.

Another exemplary location computation algorithm or triangulationtechnique may be employed in the event a scanning report is receivedfrom the serving BS and signals are received from only one neighboringBS. In this embodiment, suboptimal location determination algorithms maybe developed when a single range ring and hyperbola are available. FIG.7 is a diagram of another embodiment of the present subject illustratinglocation estimation with two site hearability and sector information.With reference to FIG. 7, a scanning report is received from a servingBS 710 from which an estimated range of the mobile or subscriber stationmay be determined and represented as a range ring 712 having a radius r.A hyperbola 722 may be determined as a function of signals received froma neighboring BS 720. In this embodiment, there will be at most twointersecting points 732, 734, one of which can be ruled out by observingthe serving sector 714 geometry, that is, the intersecting point 732inside the serving sector 714 represents the mobile or subscriberstation's location 740, and the intersecting point 734 outside theserving sector 714 fails to represent the location of the subscriberstation 740. In the event that both of the intersecting points 732, 734lie within the serving sector 714, CINR measurements may be utilized tofurther divide the serving sector into sub-sectors and to identify themost likely location. FIG. 8 is a diagram of a further embodiment of thepresent subject matter illustrating location estimation with two sitehearability and sub-sector information. With reference to FIG. 8, ascanning report may be received from the serving BS 710 from which anestimated range of the mobile or subscriber station may be determinedand represented as a range ring 712 having a radius r. A hyperbola 722may be determined as a function of signals received from the neighboringBS 720. In this embodiment, the two intersecting points 732, 734 areboth in the serving sector 714; however, CINR measurements may beutilized to divide the serving sector 714 into sub-sectors 714 a-c. Forexample, in one embodiment of the present subject matter, sub-sectors714 a-c may be determined as a function of a comparison of CINRmeasurements in the sector 714. The most likely sub-sector 714 a of theserving sector 714 may be determined and the intersecting point 732inside the most likely sub-sector 714 a represents the mobile orsubscriber station's location 740. In another embodiment, the mostlikely sub-sector 714 a may be determined as a function of comparisonsof the respective CINR measurements of the sub-sectors 714 a-c. Theintersecting point 734 outside the most likely sub-sector 714 a fails torepresent the location of the subscriber station 740. In the unlikelyevent where both of the intersecting points lie within the most likelysub-sector, or when none of the intersecting points lie in the mostlikely sub-sector, the sub-sector algorithm described with reference toFIG. 6 and subsequent exemplary pseudo-code may be utilized to ascertainthe mobile or subscriber station location. In embodiments of the presentsubject matter that receive reports and/or signals from a serving BS andtwo or more neighboring BSs, standard triangulation algorithms with onerange ring and two hyperbolas may be utilized.

Embodiments of the present subject matter may be understood through thefollowing explanation regarding timing relationships for WiMAX and/orLTE measurements. FIG. 9 is diagram of timing relationships in anembodiment of the present subject matter. With reference to FIG. 9, inone embodiment, BS₁ 910 may be a serving base station for a subscriberor mobile station MS 950. BS₂ 920, BS₃ 930, . . . , BS_(n) 940 may beneighboring base stations having a signal detectable at the MS 950.Frame marker Tx₁ from BS₁ 910 is transmitted at time t₁, frame markerTx₂ from BS₂ 920 is transmitted at time t₂, frame marker Tx₃ from BS₃930 is transmitted at time t₃, and frame marker Tx_(n) from BS_(n) 940is transmitted at time t_(n). τ₁ 911 represents the propagation delayfrom the BS₁ 910 to the MS 950, τ₂ 921 represents the propagation delayfrom the BS₂ 920 to the MS 950, τ₃ 931 represents the propagation delayfrom the BS₃ 930 to the MS 950, and τ_(n) 941 represents the propagationdelay from the BS_(n) 940 to the MS 950. It follows that the downlinkframe marker Tx₁ will be received τ₁ seconds later at the MS 950 as Rx₁,the downlink frame marker Tx₂ will be received τ₂ seconds later at theMS 950 as Rx₂, the downlink frame marker Tx₃ will be received τ₃ secondslater at the MS 950 as Rx₃, and the downlink frame marker Tx_(n) will bereceived τ_(n) seconds later at the MS 950 as Rx_(n).

Defining the time difference of Rx₂, Rx₃, and Rx_(n) relative to Rx₁ asΔ₁₂, Δ₁₃, . . . , and Δ_(1n), it follows that the MS 950 will report anRTD, Δ₁₂, Δ₁₃, . . . , and Δ_(1n) as the scanning result where RTD=2τ₁.If the ranges of the MS 950 from the base stations 910-940 are denotedby r₁, r₂, r₃, . . . , r_(n), and if c represents the speed of light,the following relationships may be provided to represent the respectiveranges:

$\begin{matrix}{r_{1} = {{\tau_{1}/c} = {{RTD}/( {2c} )}}} & (6) \\{r_{2} = {{\tau_{2}/c} = {( {\tau_{1} + \Delta_{12} - ( {t_{2} - t_{1}} )} )/c}}} & (7) \\{{r_{3} = {{\tau_{3}/c} = {( {\tau_{1} + \Delta_{13} - ( {t_{3} - t_{1}} )} )/c}}}\ldots} & (8) \\{r_{n} = {{\tau_{4}/c} = {( {\tau_{1} + \Delta_{1n} - ( {t_{n} - t_{1}} )} )/c}}} & (9)\end{matrix}$

An estimated location of the MS 950 may be determined using the rangescalculated in the relationships above. The parameters t₁, t₂, t₃, . . ., t_(n), may be determined by an NSU or as a function of othersynchronization techniques. In the event the number of available rangesis less than three, exemplary algorithms described above maysubsector/sector algorithms described in the paragraphs above may beutilized to determine the most likely location of the MS 950.Additionally, standard multilateration techniques may be employed forthree or more range rings and the techniques described in co-pendingU.S. application Ser. No. 12/292,821, similarly assigned andincorporated by reference in its entirety, may also be employed inembodiments of the present subject matter.

The n equations (Equations 7-9) may also be solved using TDOAhyperbolas. For example, h₁₂ represents a hyperbola between BS₁ 910 andBS₂ 920, h₁₃ represents a hyperbola between BS₁ 910 and BS₃ 930, andh_(1n) represents a hyperbola between BS₁ 910 and BS_(n) 940, then the nequations may be rewritten as follows:

$\begin{matrix}{h_{12} = {{r_{1} - r_{2}} = {( {{- \Delta_{12}} + ( {t_{2} - t_{1}} )} )/c}}} & (10) \\{{h_{13} = {{r_{1} - r_{3}} = {( {{- \Delta_{13}} + ( {t_{3} - t_{1}} )} )/c}}}\ldots} & (11) \\{h_{1n} = {{r_{1} - r_{n}} = {( {{- \Delta_{1n}} + ( {t_{n} - t_{1}} )} )/c}}} & (12)\end{matrix}$

While the two sets of equations may include substantially the sameinformation, the implementation is different. For example, in Equations7-9, n range rings are provided; however, in Equations 10-12, one rangering and (n−1) hyperbolas are provided. Embodiments of the presentsubject matter may utilize one or both sets and/or any combination ofthe above equations.

FIG. 10 is a schematic representation of an algorithm according to oneembodiment of the present subject matter. With reference to FIG. 10, amethod 1000 is provided for estimating a location of a subscriberstation receiving a first signal from a first BS and receiving a secondsignal from a second BS where the first and second BSs are nodes in aWiMAX or LTE network. These signals may be synchronized to a commontiming standard such as, but not limited to, a satellite navigationsystem timing standard. In embodiments including one or more NSUs, anynumber of which may be co-located with the BSs and/or may be sparselyarranged in the network, the NSU(s) may be synchronized to a timingstandard and located at predetermined locations. In this embodiment, thetiming standard may also be a satellite navigation system timingstandard, and a TOA may be determined at the NSU for the first andsecond signals. In a further embodiment, plural additional subscriberstations may be operating in the network with each or several reportingtheir respective GPS locations and subscriber station measurements tothe network to thereby allow the network to determine synchronizationbetween the BSs.

The method 1000 may include at step 1010 receiving a message from thesubscriber station, the message containing a first information and asecond information, and at step 1020, determining a range ring from thefirst BS using the first information. In one embodiment, the message maybe a scanning result report message. Further, the first information mayinclude an RTD time value between the subscriber station and the firstBS, and the second information may include a relative time delay valueobserved at the subscriber station between the first and second signals.In another embodiment, the message may also include additionalinformation such as, but not limited to, a subscriber identification, aCINR value for at least one of the first and second BSs, and/or an RSSIvalue for at least one of the first and second BSs. Of course, thesemessages may be used by the WiMAX or LTE network for determining handoffoperations for the subscriber station.

At step 1030, a location hyperbola may be determined using the secondinformation where the location hyperbola has the first and second BS asfoci. An estimated location of the subscriber station may be determinedat step 1040 using the range ring and hyperbola. In one embodiment, thesubscriber station may be A-GPS capable and the timing offset betweenthe first and second signals may be determined from the subscriberstation message and/or the respective location hyperbola determinedbased on the timing offset. In an additional embodiment, step 1040 mayinclude determining a serving sector of the first BS for the subscriberstation and estimating a location of the subscriber station as a pointof intersection of the range ring and location hyperbola that is withinthe serving sector. In another embodiment, step 1040 may includedetermining a serving sector of the first BS for the subscriber station,and if the range ring and location hyperbola intersect plural timeswithin the serving sector, (i) determining plural sub-sectors for theserving sector, (ii) determining from the message a CINR for each of afirst and a second neighboring sector to the serving sector, (iii)determining a most likely sub-sector from the plural sub-sectors basedon a comparison of the CINR for the first and second neighboringsectors, and (iv) estimating a location of the subscriber station as apoint of intersection of the range ring and location hyperbola that iswithin the most likely sub-sector. In yet a further embodiment of thepresent subject matter, step 1040 may include determining a secondlocation hyperbola using the second information wherein the secondlocation hyperbola has the first BS and a third BS as foci, andestimating a location of the subscriber station using the range ring,location hyperbola, and the second location hyperbola.

FIG. 11 is a schematic representation of an algorithm according toanother embodiment of the present subject matter. With reference to FIG.11, a method 1100 is provided for estimating a location of a subscriberstation receiving a first signal from a first BS, receiving a secondsignal from a second BS, and receiving a third signal from a third BSwhere the first, second, and third BSs are nodes in a WiMAX or LTEnetwork. The method 1100 may include, at step 1110 receiving a messagecontaining a first information and a second information from thesubscriber station, and at step 1120, determining a range ring from thefirst BS using the first information. At step 1130, a location hyperbolamay be determined using the second information where the locationhyperbola has the second and third BSs as foci. A location of thesubscriber station may be estimated at step 1140 using the range ringand location hyperbola.

FIG. 12 is a schematic representation of an algorithm according to afurther embodiment of the present subject matter. With reference to FIG.12, a method 1200 is provided for estimating a location of a subscriberstation receiving a signal from a BS where the BS is a node in a WiMAXor LTE network. The method 1200 may comprise at step 1210, receivingfrom the subscriber station a message containing a first information anda second information, and at step 1220 determining a range ring from theBS using the first information. In one embodiment, the message may be ascanning result report message. Further, the first information mayinclude an RTD time value between the subscriber station and the firstBS. Of course, these messages may be used by the WiMAX or LTE networkfor determining handoff operations for the subscriber station. At step1230, a serving sector of the base station may be determined for thesubscriber station, and plural sub-sectors determined for the servingsector at step 1240. At step 1250, a CINR may be determined from thesecond information for each of a first and a second neighboring sectorto the serving sector. In one embodiment, the CINR may be reported bythe subscriber station periodically or by demand. At step 1260, a mostlikely sub-sector may then be determined from the plural sub-sectorsbased on a comparison of the CINR for the first and second neighboringsectors. At step 1270 a location of the subscriber station may beestimated as a point of intersection of the range ring and a bisector ofthe most likely sub-sector.

FIG. 13 is a schematic representation of an algorithm according to anadditional embodiment of the present subject matter. With reference toFIG. 13, a method 1300 is provided for estimating a location of asubscriber station operating in a wireless network. The method 1300 mayinclude transmitting from a network location device to a first BS arequest for network measurement data at step 1310, and transmitting fromthe first BS to the subscriber station a message to trigger thesubscriber station to scan the wireless network at step 1320. At step1330, a scanning result message containing information characterizingthe first BS and a second BS may be transmitted from the subscriberstation to said first BS. In one embodiment, the scanning result messagemay further include a round trip time delay, a relative delay, a CINR,and/or an RSSI. At step 1340, information from the scanning resultmessage may then be transmitted from the first BS to the networklocation device. A location for the subscriber station may then beestimated at the network location device based at least on theinformation from the scanning result message at step 1350. In oneembodiment, step 1350 may include determining a range ring from thefirst BS, determining a location hyperbola having the first and secondBSs as foci, and estimating a location of the subscriber station usingthe range ring and location hyperbola. Of course, any number of thesteps described above and shown in FIGS. 10-13 may be implemented in thesystems depicted in FIGS. 3-4 and 6-8.

By way of a non-limiting example, with reference to FIGS. 3 and 7, anexemplary system 300 is provided for estimating a location of asubscriber station 310 receiving a first signal from a first BS 322 andreceiving a second signal from a second BS (not shown) where the firstand second B Ss are nodes in a WiMAX or LTE network. These signals maybe synchronized to a common timing standard such as, but not limited to,a satellite navigation system timing standard. In embodiments includingone or more NSUs 342, any number of which may be co-located with the BSs322 and/or may be sparsely arranged in the network, the NSU(s) 342 maybe synchronized to a timing standard and located at predeterminedlocations. In one embodiment, the timing standard may also be asatellite navigation system timing standard, and a TOA may be determinedat the NSU 342 for the first and second signals. In a furtherembodiment, plural additional subscriber stations (not shown) may beoperating in the network with each or several reporting their respectiveGPS locations and subscriber station measurements to the network tothereby allow the network to determine synchronization between the BSs.

The first BS 322 may include a receiver for receiving from thesubscriber station 310 a message containing first and secondinformation. The first information may include an RTD time value betweenthe subscriber station 310 and the first BS 322, and the secondinformation may include a relative time delay value observed at thesubscriber station 310 between the first and second signals. In anotherembodiment, the message may also include additional information such as,but not limited to, a subscriber identification, a CINR value for atleast one of the first and second BSs, and/or an RSSI value for at leastone of the first and second BSs. Of course, these messages may be usedby the WiMAX or LTE network for determining handoff operations for thesubscriber station 310.

The system 300 may include circuitry at the LIS 302 and/or PDE 332 fordetermining a range ring from the first BS using the first informationand circuitry at the LIS 302 and/or PDE 332 for determining a locationhyperbola using the second information wherein the location hyperbolahas the first and second BSs as foci. Further, the system 300 mayinclude circuitry at the LIS 302 and/or PDE 332 for estimating alocation of the subscriber station 310 using the range ring the saidlocation hyperbola. In one embodiment, the subscriber station 310 may beA-GPS capable and the timing offset between the first and second signalsmay be determined from the subscriber station message and/or therespective location hyperbola determined based on the timing offset. Inan additional embodiment, the system 300 may include circuitry fordetermining a serving sector of the first BS 322 for the subscriberstation 310 and estimating a location of the subscriber station 310 as apoint of intersection of the range ring and location hyperbola that iswithin the serving sector. In another embodiment, the system 300 mayinclude circuitry for determining a serving sector of the first BS 322for the subscriber station 310, and if the range ring and locationhyperbola intersect plural times within the serving sector, (i)determining plural sub-sectors for the serving sector, (ii) determiningfrom the message a CINR for each of a first and a second neighboringsector to the serving sector, (iii) determining a most likely sub-sectorfrom the plural sub-sectors based on a comparison of the CINR for thefirst and second neighboring sectors, and (iv) estimating a location ofthe subscriber station 310 as a point of intersection of the range ringand location hyperbola that is within the most likely sub-sector. In yeta further embodiment of the present subject matter, the system 300 mayinclude circuitry for determining a second location hyperbola using thesecond information wherein the second location hyperbola has the firstBS 322 and a third BS (not shown) as foci, and estimating a location ofthe subscriber station 310 using the range ring, location hyperbola, andthe second location hyperbola.

As another example and with reference to FIGS. 3 and 8, an exemplarysystem 300 is provided for estimating a location of a subscriber station310 receiving a signal from a BS 322 where the BS 322 is a node in aWiMAX or LTE network. The BS 322 may include a receiver for receivingfrom the subscriber station 310 a message containing first and secondinformation. In one embodiment, the message may be a scanning resultreport message. Further, the first information may include an RTD timevalue between the subscriber station 310 and the BS 322. Of course,these messages may be used by the WiMAX or LTE network for determininghandoff operations for the subscriber station 310. The system 300 mayinclude circuitry at the LIS 302 and/or PDE 332 for determining a rangering from the BS 322 using the first information, and include circuitryat the LIS 302 and/or PDE 332 for determining a serving sector of the BS322 for the subscriber station 310, circuitry for determining pluralsub-sectors for the serving sector, circuitry for determining from thesecond information a CINR for each of a first and a second neighboringsector to the serving sector, and circuitry for determining a mostlikely sub-sector from the plural sub-sectors based on a comparison ofthe CINR for the first and second neighboring sectors. Further, thesystem 300 may include circuitry at the LIS 302 and/or PDE 332 forestimating a location of the subscriber station 310 as a point ofintersection of the range ring and a bisector of the most likelysub-sector.

As yet another example and with continued reference to FIGS. 3 and 7, anexemplary system 300 may be provided for estimating a location of asubscriber station 310 operating in a wireless network. The system 300may include a network location device 302 having a first transmitter fortransmitting to a first BS 322 a request for network measurement data.The first BS may include a second transmitter to transmit to thesubscriber station 310 a message to trigger the subscriber station 310to scan the wireless network. The subscriber station 310 may alsoinclude a third transmitter to transmit to the first BS 322 a scanningresult message containing information characterizing the first BS 322and a second BS (not shown). In one embodiment, the scanning resultmessage may further include a round trip time delay, a relative delay, aCINR, and/or an RSSI. The first BS 322 may further include a fourthtransmitter to transmit to the network location device 302 informationfrom the scanning result message. In one embodiment the second andfourth transmitters may be the same. The system 300 may also includecircuitry for estimating at the network location device 302 and/or PDE332 a location for the subscriber station 310 based at least on theinformation from the scanning result message. In one embodiment, thenetwork location device 302 and/or PDE 332 may include circuitry fordetermining a range ring from the first BS 322, circuitry fordetermining a location hyperbola having the first and second BSs asfoci, and circuitry for estimating a location of the subscriber station310 using the range ring and location hyperbola.

As shown by the various configurations and embodiments illustrated inFIGS. 1-13, a system and method for locating subscriber stations in aWiMAX or LTE network have been described.

While preferred embodiments of the present subject matter have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

1. A method for estimating a location of a subscriber station operatingin a wireless network, comprising the steps of: (a) transmitting from anetwork location device to a first base station a request for networkmeasurement data; (b) transmitting from said first base station to saidsubscriber station a message to trigger said subscriber station to scansaid wireless network; (c) transmitting from said subscriber station tosaid first base station a scanning result message containing informationcharacterizing said first base station and a second base station; (d)transmitting from said first base station to said network locationdevice information from said scanning result message; and (e) estimatingat said network location device a location for said subscriber stationbased at least on said information from said scanning result message. 2.The method of claim 1 wherein said scanning result message includes around trip time delay, a relative delay, a carrier to interference noiseratio, and a received signal strength indicator.
 3. The method of claim1 wherein the step of estimating a location for said subscriber stationincludes: (i) determining a range ring from said first base station;(ii) determining a location hyperbola having said first and said secondbase stations as foci; and (iii) estimating a location of saidsubscriber station using said range ring and said location hyperbola. 4.The method of claim 1 wherein signals sent from said first and secondbase stations are synchronized to a common timing standard.
 5. Themethod of claim 1 wherein said wireless network is a WiMAX or LTEnetwork.
 6. The method of claim 1 wherein said WiMAX or LTE networkincludes a Network Synchronization Unit (“NSU”) wherein said NSU issynchronized to a timing standard and located at a predeterminedlocation.
 7. The method of claim 6 wherein said WiMAX or LTE networkincludes a predetermined number N base stations and a predeterminednumber M NSUs wherein N>1 and N>M.
 8. The method of claim 1 wherein saidsubscriber station is an Assisted-Global Positioning System (“A-GPS”)enabled subscriber station, and wherein a timing offset between saidfirst and second signals is determined from said subscriber stationmessage.
 9. The method of claim 1 wherein plural additional subscriberstations are operating in said WiMAX or LTE network with each reportingtheir Global Positioning System (“GPS”) locations and subscriber stationmeasurements to said network to thereby allow said network to determinesynchronization between said base stations.
 10. A system for estimatinga location of a subscriber station operating in a wireless network,comprising: (a) a network location device including a first transmitterfor transmitting to a first base station a request for networkmeasurement data; (b) said first base station including a secondtransmitter to transmit to said subscriber station a message to triggersaid subscriber station to scan said wireless network; (c) saidsubscriber station including a third transmitter to transmit to saidfirst base station a scanning result message containing informationcharacterizing said first base station and a second base station; (d)said first base station including a fourth transmitter to transmit tosaid network location device information from said scanning resultmessage; and (e) circuitry for estimating at said network locationdevice a location for said subscriber station based at least on saidinformation from said scanning result message.
 11. The system of claim10 wherein said scanning result message includes a round trip timedelay, a relative delay, a carrier to interference noise ratio, and areceived signal strength indicator.
 12. The system of claim 10 whereinsaid circuitry for estimating a location for said subscriber stationincludes: (i) circuitry for determining a range ring from said firstbase station; (ii) circuitry for determining a location hyperbola havingsaid first and said second base stations as foci; and (iii) circuitryfor estimating a location of said subscriber station using said rangering and said location hyperbola.
 13. The system of claim 10 whereinsaid second transmitter and said fourth transmitter are the same. 14.The system of claim 10 wherein signals sent from said first and secondbase stations are synchronized to a common timing standard.
 15. Thesystem of claim 10 wherein said wireless network is a WiMAX or LTEnetwork.
 16. The system of claim 10 wherein said WiMAX or LTE networkincludes a Network Synchronization Unit (“NSU”) wherein said NSU issynchronized to a timing standard and located at a predeterminedlocation.
 17. The system of claim 16 wherein said WiMAX or LTE networkincludes a predetermined number N base stations and a predeterminednumber M NSUs wherein N>1 and N>M.
 18. The system of claim 10 whereinsaid subscriber station is an Assisted-Global Positioning System(“A-GPS”) enabled subscriber station, and wherein a timing offsetbetween said first and second signals is determined from said subscriberstation message.
 19. The system of claim 10 wherein plural additionalsubscriber stations are operating in said WiMAX or LTE network with eachreporting their Global Positioning System (“GPS”) locations andsubscriber station measurements to said network to thereby allow saidnetwork to determine synchronization between said base stations.